Photosensitive solid-state image intensifier



Nov. 9, 1965 TADAO KOHASHI 3, 7, 8

PHOTOSENSITIVE SOLID-STATE IMAGE INTENSIFIER Filed Dec. 14, 1961 2 Sheets-Sheet l ,2 -1 l 1 31 3 1 33 E. i EN 4. T'fl'fi ADJ, f V| 4 9 mafia 1 L2 l;:| @95 3 34 3 5 36 37 INVENTOR TADAO KOHASHI Nov. 9, 1965 TADAO KOHASHI PHOTOSENSITIVE SOLID-STATE IMAGE INTENSIFIER Filed Dec. 14, 1961 2 Sheets-Sheet 2 4 1.5 Ema.

1 v 8 g IMP r 42 1 4 IMP.

INVENTOR TADAO KOHASHI BY M AG ENT United States Patent 3,217,168 PHOTOSENSITIVE SOLID-STATE IMAGE INTENSIFIER Tadao Kohashi, Kadoma-cho, Kitakawachi-gun, Osaka, Japan, assignor to North American Philips Company, Inc., New York, N .Y., a corporation of Delaware Filed Dec. 14, 1961, Ser. No. 159,358 Claims priority, application Japan, Dec. 29, 1960, 35/ 51,639 11 Claims. (Cl. 250213) This invention relates to a device comprising a solidstate image intensifier connected to a voltage supply apparatus, said intensifier comprising a photo-conductive layer between a luminescent layer having a luminance varying with its electric field intensity and a neutral or fixed impedance layer and also comprising electrodes for applying an electric supply voltage, whereof a first electrode is arranged on the outer side of the luminescent layer and a second electrode is arranged on the outer side of the neutral impedance layer and a third electrode lying between the luminescent layer and the neutral impedance layer consists of electrically interconnected linear, electrically conductive parts, which may be interconnected groupwise and which are in electrical contact with the photo-conductive layer and constitute a lineor net-shaped grid.

A solid-state image intensifier of the kind set forth is described in a prior application of the applicant, Serial No. 109,055, filed May 10, 1961, now Patent No. 3,169,192. The third electrode contacting the photo-conductive layer may consist of a grid of parallel, equidistant, conductive paths, for example of a metal, which are applied to the top face or underneath the photoconductive layer. Instead of using paths use may be made of metal wires, which are preferably embedded in the photo-conductive layer. These paths or wires may all be connected with each other at the ends, so that they are at the same potential, but they may, as an alternative, be connected alternately with each other, so that two electrical groups of paths or wires are formed. The latter arrangement is used in case it is desired when the intensifier is fed by alternating current to supply the photo-conductive layer with a direct bias voltage with a view to the greater sensitivity of a photo-conductive layer formed by a photo-conductive material and a binder to direct current. This may be achieved by including rectifiers of opposite polarities or direct-voltage sources in the connection of the two groups of the third electrode. The third electrode may furthermore be formed by a net-shaped grid, preferably having square meshes, formed by conductive paths on or below the photo-conductive layer or embedded herein in the form of a net of metal wires.

In the said prior application it has been pointed out that such a solid-state image intensifier is capable of producing a positive or a negative luminescent image of a primary radiation image projected onto the photoconductive layer according as the supply voltage is fed to the first or to the third electrode, while the second electrode is directly connected to the first electrode or, according as the supply voltage is fed to the first and to the second electrode, while the third electrode is connected directly to the first electrode.

The present invention is based on the recognition of the fact that by varying the relationship between the voltages fed to the second electrode and to the third electrode, with respect to the first electrode, not only a variation of the positive image into the negative image and conversely can be carried out, but also the characteristic curve of the solid-state image intensifier, indicating the relationship between the intensity of the primary 3 ,Z I 7,168 Patented Nov. 9, 1 965 ice radiation and the resultant luminance of the luminescence image, can be varied within wide limits. This variation applies in particular to the steepness of the said characteristic curve, which determines the gradation of the luminescence image.

The device according to the invention is characterized in that the solid-state image intensifier is connected to the current supply apparatus so that the voltage between the first electrode and the second electrode V and the voltage between the first electrode and the third electrode V differ both from zero and from each other, while provision is made of means for the adjustable variation of the difference between the two voltages (value and/or polarity in the case of direct voltage; amplitude and phase in the case of alternating voltage).

It should be noted that the solid-state image intensifier in the embodiment according to the invention and of the kind described in the aforesaid prior application may be suitable for alternating-voltage supply and also for direct-voltage supply, in which latter case the luminescent layer, the neutral impedance layer and any thin lightscreening and/or reflecting layers between the photoconductive layer and the luminescent layer must have some direct-current conductivity.

In a preferred embodiment of the device according to the invention, the said voltages fed by the supply apparatus to the electrodes of the solid-state image intensifier are such that, in the case of alternating voltages, the phase difference is more than and in the case of direct voltages the polarities are opposite. It is advantageous to choose the voltages so that in the state of minimum conductivity of the photo-conductive layer the voltage between the first and the second electrode V itself and in the state of maximum conductivity of the photo-conductive layer the voltage between the first and the third electrode V itself are capable of exciting the luminescent layer to visible luminance or up to the limit of visible luminance. In order that the invention may be clearly understood and readily carried into effect, it will now be desired more fully with reference to the accompanying drawing, which shows a few embodiments.

FIG. 1 shows diagrammatically a cross sectional view of a solid-state image intensifier having three electrodes connected to a supply apparatus and FIG. 2 shows diagrammatically the electric diagram of a group of elements of the solid-state image intensifier shown in FIG. 1, which elements, in common, define an image point of the reproduced image.

FIG. 3 shows the diagram of one embodiment of the supply apparatus shown in the device of FIG. 2, this apparatus being connected to the electrodes of the solidstate image intensifier indicated only by the electrodes and FIG. 4 shows a different embodiment of the supply apparatus.

FIG. 5 shows a further embodiment of the device according to the invention, in which also the solid-state image intensifier is indicated symbolically only by its electrodes.

In the embodiments shown in the various figures the same parts and elements are found for a large part, particularly with respect to the solid-state image intensifier. These elements or parts are therefore designated in the various figures by the same reference numerals. It should furthermore be noted that various dimensions of the solidstate image intensifier, particularly those referring to the thickness of various layers are not shown with their correct ratio in FIGS. 1 and 2; if necessary suitable numerical values are given for several dimensions hereinafter.

The device according to the invention illustrated in FIGS. 1 and 2 comprises a solid-state image intensifier 1, which is connected to a supply apparatus 2 which supplies a voltage which in view of the construction of the solid-state image intensifier to be described is an alternating voltage. The intensifier 1 comprises a number of layers applied one over the other in the following order of succession, viewed from bottom to top: a, transparent support 3, a transparent plane electrode 4, a luminescent layer 5, a reflecting layer 6, a light-screening layer 7, a photo-conductive layer 8 with an electrode of parallel metal wires 9 embedded therein, a neutral transparent impedance layer 10 and a plane transparent electrode 11.

The plane electrode 4 (first electrode) may consist of metal applied by vaporisation to the supporting plate 3, for example gold, or, particularly when the support 3 is formed by a glass plate, of a layer of conductive tin oxide.

The luminescent layer 5, which has a thickness of, for example, 50 may consist of electro-luminescent material, for example zinc sulphide activated by copper and aluminum. and a binder, for example an epoxy resin. The thin reflecting layer 6, which serves to reflect to the optimum the luminescent light produced in the layer 5 towards the supporting plate 3, may consist of a white reflecting powder, for example barium titanate or titanium dioxide and a binder, which may also be an epoxy resin. This reflecting layer may have a thickness of about 20 The opaque layer 7, which serves to avoid optical feedback due to possible action of luminescent light from the layer 5 on the photo-conductive layer 8, consists of a binder, for example an epoxy resin, to which carbon powder is added. The composition of this layer must, be such that in the direction of the layer substantially no electric conductivity is found. In most cases an addition of 5% by volume of carbon powder to the binder, with a thickness of the layer of about p, will provide an adequate light-screening effect. In order to minimise the impedance in the direction of thickness of this light-screening layer 7, this layer may contain furthermore a material having a high dielectric constant, for example barium titanate.

The photo-conductive layer 8 consists of a photo-conductive material, for example cadmium sulphide activated by copper and chlorine or cadmium sulphoselenide or cadmium selenide, and a binder, for example an epoxy resin. In this layer 8 are embedded, in parallel position, and at equal distances of 250;, tungsten wires 9 of a diameter of 10 In FIG. 1 the thickness of these wires 9 is shown on an excessive scale. The wires may be located in the central plane of the photo-conductive layer 8, but it is more advantageous to apply them to the top face of the layer 8, so that they have an optical screening effect for the parts of the photo-conductive layer 8 lying directly underneath these wires. The wires 9 are electrically connected to each other at one side of the intensifier 1 and constitute together the third electrode of the solid-state image intensifier 1.

The neutral impedance layer 10, which may have a thickness of about 70 1., consists of a transparent synthetic resin, preferably having low electric losses and a high dielectric constant, for example an epoxy resin. This layer may, however, consist of glass; it may be formed, for example by a glass foil which is secured to the photo-conductive layer 8 for example by means of a transparent adhesive. The electrode 11 extending over this neutral impedance layer and forming the second electrode of the solid-state image intensifier 1 may consist of a transparent metal layer, applied for example by vaporisation, or of conductive tin oxide. It is not always required for this electrode to be transparent, since if the solid-state image intensifier is to be used with X-rays, the electrode 11 preferably consists of aluminum, having a thickness such that this electrode does not allow visible light to pass.

In accordance with the invention, the supply appa ratus 2 is arranged and the electrodes of the solid-state image intensifier 1 are connected to this supply apparatus so that the voltage V between the first and the second electrode and the voltage V between the first and the third electrode both differ from zero and from each other. Since we are concerned in FIG. 1 with a solid-state image intensifier fed by alternating voltage, the later means that the voltages V and V have different amplitudes and/or have a phase ditference. The supply apparatus 2 is furthermore arranged so that the ditference between the voltages V and V can be varied and be adjusted to a desired value.

The solid-state image intensifier in the device according to the invention is based on the fact that, according as the conductivity of the photo-conductive layer 8 is lower or higher, which conductivity is locally acted upon by a primary radiation image projected through the electrode 11 and the neutral impedance layer 10 onto the photo-conductive layer 8 (this image is symbolically designated in the figures by L the electric field in the luminescent layer 5 resulting from the voltage V between the first and the second electrode (electrodes 4 and 11) covers larger or smaller regions of this layer respectively, the electric field strength also being increased or decreased respectively, whereas the electric field in the layer 5 due to the voltage V between the first and the third electrode (electrodes 4 and 9) covers smaller or larger regions of this layer respectively. The operation of the photo-conductive layer may, to some extent, be compared with that of a control-grid in an imaginary electron valve, in which the diameter of the grid wires is varied while the pitch is maintained, this variation in diameter being locally correlated to the local intensity of the primary radiation image L Referring to FIG. 1, reference numeral 12 designates an elementary cell of the solid-state image intensifier 1, which cell defines an image point of the image (indicated by the symbol L in the figures), reproduced by the luminescent layer 5 and corresponding to the primary radiation image L projected onto the photoconductive layer 8. This elementary cell comprises a vertical column of the image intensifier located between two successive wires 9 of the third electrode, which is limited in front of and behind the plane of the drawing in FIG. 1 by vertical planes transversely to the wires 9, spaced apart by a distance equal to the distance between the successive wires 9. FIG. 2 shows a largely simplified electric diagram of such an elementary cell of the solid-state image intensifier 1. The part of the photo-conductive layer 8 in such an elementary cell constitutes a resistance 20 connecting the segments of successive wires 9, the resistance value in the unexposed state (absence of L being comparatively high and decreasing with an incraesing exposure. Each point of this resistance is capacitatively coupled on the one hand with the electrode 4 and on the other hand with the electrode 11, with which electrodes also the said segments of the wires 9' are capacitatively coupled. Although we are concerned here with a network having distributed impedances, a non-essential simplification permits of considering this network, as in FIG. 2, as being composed of lumped impedances. In FIG. 2 the capacitors AC represent the capacitative coupling of the parts of the said resistance 20 with the electrode 11; these capacitors are formed by small vertical columns of the neutral impedance layer 10. The capacitors AC represent the capacitative coupling of the resistance 20 with the electrode 4; these capacitors are formed by small vertical columns of the luminescent layer 5 and the intermediate layers 6 and 7. Owing to the small thickness or impedance in the direction of thickness of the two last-mentioned layers the capacitors AC are mainly determined by the luminescent layer 5. The capacitors 21 and 22, which represent the capacities between thesegments of the wires 9 and the electrode 4 and 11 respectively, constitute in fact a non-useful load of the supply apparatus 2, to which the electrodes of the solidstate image intensifier 1 are connected. The capacity of these capacitors 21 and 22 may be reduced by providing a greater thickness of the layers 5, 6, 7 and at the area of the wires 9 than at the areas between these wires. By arranging the wires 9, if they have a smaller diameter than the thickness of the photo-conductive layer 8, on the top face of the layer 8, it is ensured that the capacity of the capacitors 21 is minimized. Since these contain luminescent material, just these capacitors are the greatest source of disturbances in the reproduced image L By feeding to the second and the third electrode (electrodes 11 and 9 respectively) by means of the supply appartus, a voltage V and V respectively, with respect to the first electrode (electrode 4), the voltage E across the capacitors AC which are connected to points of the resistance lying at a given distance from the wire segments 9, is determined mainly by the distribution of the voltage V across the series-connected capacitors AC and AC and is substantially independent of the voltage V in the dark state (absence of L when the value of the resistance 20 is high. However, when the photo-conductive layer 8 is strongly irradiated, so that the value of the resistance 20 becomes very small and hence the element of the photo-conductive layer 8 represented by this resistance may be considered as an equipotential plane being at the potential of the wires 9, all capacitors AC have produced across them a voltage which is substantially equal to V When the photo-conductive layer is exposed to a radiation intensity lying between the aforesaid extreme values, the voltage E across the capacitors AC will shift constantly farther towards V with an increasing radiation intensity and this first with those capacitors AC which are nearest the wire segments 9. This results in that by irradiation of an element of the photo-conductive layer 8 the part of the luminescent layer 5 lying underneath it exhibits a change in the luminance, which may Vary between the luminance of the layer 5 at a supply voltage equal to the part of the voltage V obtained across the capacitors AC owing to the series combination of the capacitors AC and AC and the luminance of the layer 5 with a voltage V over-all the capacitors AC It will now be obvious that by the choice of V and V the characteristic curve of the solid-state image intensifier 1 can be acted upon.

If V and V are in phase and if the amplitude of V evceeds the amplitude of the aforesaid voltage E, obtained by the division of V the image reproduced by the intensifier 1 (image L is a positive image of the primary radiation image L This image L appears on a more or less bright background according as V and hence also E is higher and thereby gives rise, in itself, to a luminance of the layer 5. The contrast in the image L is the greater, the more V exceeds E. By the adjustment of V and V the contrast can thus be adjusted at will, provided the aforesaid conditions are maintained.

If V and V are in phase, but if the amplitude of V is smaller than that of the said voltage E and if the voltage E in itself suffices for exciting the layer 5 to luminesce, the exposure of the photo-conductive layer 8 to a primary radiation image L will produce on the luminescent layer 5 a negative image L or an inverted image i.e. having inverted brightness. The contrast in this negative image is greater according as the amplitudes of V and E are different.

An interesting situation comes up when V and V with respect to the electrode 4 (first electrode) are more or less oppositely directed i.e. have a phase difference of at least 90, preferably of 180, while the amplitudes of the voltages V and E are both adequate for exciting alone the luminescent layer 5 to luminesce. A radiation image L projected onto the photo-conductive layer 8 will then be reproduced by the layer 5 partly in the form of a negative image and partly in the form of a positive image.

The negative image corresponds to the parts of the primary image L having low radiation intensity, whereas the positive part is obtained from the parts of the primary radiation image of high radiation intensity. The intensity of L with which the negative image changes over to the positive image (transition intensity) depends upon the ratio between E and V The transition intensity is shifted towards lower intensities of L according as E is higher and V is lower and is shifted towards higher intensities of L according as E is lower and V is higher. Since E, as described above, is in direct relationship to V the transition intensity can be shifted at will by adjustment of V and V If, finally, V and V are more or less in phase opposition and if the amplitude of the latter is such that the partial voltage E in itself does not suffice to excite the luminescent layer 5 to luminesce, a primary radiation image on the photo-conductive layer 8 results in a luminance image in the layer 5 which is a positive image of the primary radiation image, this positive image appearing, however, in contrast to the first-mentioned case, on a dark background. Thus the contrast of the positive image thus obtained is greater than in the first-mentioned case and this contrast is the greater, the larger is the amplitude of V From the foregoing it will be obvious that an image intensifying device capable of being matched to different conditions and desires can be obtained by means of a solid-state image intensifier of the kind shown in FIG. 1, comprising an apertured third electrode in contact with the photo-conductive layer and fed by different voltages V and V provision being made of means for an adjustable variation of the difference between these voltages.

FIG. 3 shows an advantageous embodiment of the device according to the invention, in which the construction of the supply apparatus 2, to which the solid-state image intensifier 1, indicated only by the electrodes 4, 9 and 11, is connected is illustrated by a block diagram. The supply apparatus 2 of the device shown in FIG. 3 comprises a variable alternating-voltage source 3 1, supplying the frequencyand amplitude-variable input voltage for a first amplifier 32 having an adjustable amplification. The output of the amplifier 32 is connected to a transformer 33, the secondary Winding of which is connected to the electrodes '4 and 11 (first electrode and second electrode) of the solid-state image intensifier 1, between which it produces a voltage V The voltage of the alternating-voltage source 31 is also fed to a second adjustable amplifier 35 via an adjustable phase-shift device 34, which may be formed in known manner by the series combination of a capacitor and a resistor, but which may be constructed in a different manner. The output of the amplifier 35 is connected to a transformer 36, the secondary winding of which is connected via a commutator 37 to the electrodes 4 and 9 (first electrode and third electrode) of the image intensifier 1, to which electrodes a voltage V is fed. It will be obvious that owing to the controllability of the amplification obtained by the amplifiers 32 and 35 and owing to the controllability of the phase difference between the input voltages fed to the amplifiers 32 and 35 by means of the phaseshift device 34 the voltages V and V can be varied at will with respect to their amplitude and phase-difference. In order to obtain the simplest structure of the phaseshift device 34, the supply circuit of the electrodes 4 and 9 includes a commutator 37, which varies the phase difference between the voltages V and V by by switching over. This commutator could also be included in the supply circuit of the electrodes 4 and 11.

It should be noted that in the foregoing explanation given with reference to FIG. 2 for the influence of V and V on the characteristic curve of the solid-state image intensifier 1, reference is mainly made to the in-phase and the opposite-phase condition of the voltages V and V but that it should be considered that another phase difference between these voltages is possible and has its influence on the characteristic curve. The effect described above for voltages V and V of opposite phases occurs when the phase difference between these voltages exceeds 90"; the greater this phase difference, the greater is the effect. In the device shown in FIG. 3 this phase difference can be completely adjusted at will owing to the introduction of the phase-shift device 34 and the commutator 37.

FIG. 4 shows in a diagram a further composition of the supply apparatus 2. One terminal of a variable alternating-voltage source 41 is directly connected to the electrode 11 of the image intensifier 1. The other terminal of the alternating-voltage source 41 is connected via a variable impedance 42 to the electrode 4 and via a second variable impedance 43 to the electrode 9 of the image intensifier. The impedances 4 2 and 43 may be formed by adjustable resistors, inductors or capacitors or combinations thereof. The impedance 42 is furthermore shunted by a short-circuit switch 44 and the impedance 43 is shunted by a short-circuit switch 45. When the two switches are open and when the impedances 42 and 43 provide a phase shift having a difference of not more than 90, the voltages V and V fed to the electrodes of the intensifier may be considered to some extent as inphase voltages, while their amplitude ratio can be controlled by the adjustment of the impedances 42 and 43. When the switch 44 is closed, the impedance 43 produces an electric feedback, since with an increasing irradiation of the photo-conductive layer in the intensifier 1 the current passing from the electrode 11 to the electrode 9 and subsequently through the impedance 43 increases, resulting in an increase of the amplitude of V When the alternating-voltage source 41 and the impedance 43 are adjusted so that the intensifier 1 produces a negative image, this means a feedback which attenuates the contrast in the reproduced image.

However, 'when the switch 44 is opened and the switch 45 closed, V and V have a more or less opposite sense, if at least the impedance 43 does not produce a phaseshift of more than 90; thus the above-mentioned effects can be obtained. Also in this case an electric feed-back occurs, i.e. owing to the presence of the impedance 42. This feedback is, in this case, positive, which :gives rise to an enhancement of the contrast.

The device according to the invention illustrated in FIG. differs from that shown in FIG. 1 in that the electrode wires 9 are not all connected to each other, but alternately, so that two electric groups are formed. Between these two groups is connected a direct-voltage source 51, which feeds an adjustable direct bias voltage to these groups. Each of the two groups is furthermore connected via a capacitor 52 and 53 respectively to the same output terminal of the supply apparatus 2, which supplies a voltage V relative to the terminal to which the electrode 4 (first electrode) of the image intensifier is connected. The capacitors 52 and 53 prevent a direct short-circuit of the direct voltage source 51 and also a short-circuit of this source via the supply apparatus 2 and the intensifier 1. If the latter cannot convey direct current between the output terminals and between the electrodes respectively, one of the capacitors 52 or 53 may be omitted. The bias voltage fed by the direct voltage source 51 via the two groups of the electrodes 9 to the photo-conductive layer of the intensifier 1 serves for enhancing in known manner the sensitivity of the photo-conductive layer, which is higher for direct voltages than for alternating voltages. By adjusting the bias voltage supplied by the direct voltage source 51, the sensitivity of the photo-conductive layer in the intensifier can be controlled. It will be obvious that the bias voltage of the two electric groups of the wires of the third electrode 9 may be obtained by a different arrangement of the direct voltage source 51, for example by including the latter in only one of the connections of the supply apparatus 2 to the two groups of the electrode 9. The direct voltage source may, as is known, be replaced by oppositely directed rectifiers in the two connections.

The invention is not restricted to the use of the embodiment of a solid-state image intensifier as described with reference to FIG. 1. It is, for example, not necessary to sandwich between the luminescent layer and the photo-conductive layer a layer which screens the latter completely'from the light produced in the former. By using optical feedback between the luminescent layer and the photo-conductive layer, in which case known measures should be taken to restrict the optical feedback locally to photo-conductive elements and the luminescent elements controlled by said photo-conductive elements, an intensified contrast of the reproduced image can be obtained if this image is a positive image, whereas in the case of a reproduced image in the form of a negative image the optical feedback results in a reduction of contrast. If the solid-state image intensifier in the device according to the invention is fed so that the reproduced image is a positive image, the optical feedback may give rise to instability, which then becomes manifest at an intensity of the primary radiation image which depends upon the supply voltages V and V Thus a memory effect may be obtained, in which the reproduced image is stored in the form of bright and dark parts, i.e. without intermediate shadings. This stored image may be erased, for example by reducing the voltage V so that the image intensifier arrives in the region of a negative image reproduction, the feedback becoming then negative and the image intensifier being capable of returning to its initial state.

The device according to the invention may furthermore be provided with a solid-state image intensifier operated by direct voltage. In this case the luminescent layer and the neutral impedance layer must have a sufficient amount of direct-current conductivity; the supply apparatus can then feed direct voltages V and V to the electrodes of the intensifier, these voltages being required to be adjustable in value and polarity.

What is claimed is:

1. Apparatus comprising a solid-state image intensifier; said intensifier including a first electrode, an electric-field-responsive luminescent layer over the first electrode, a radiation-responsive photoconductive layer over the luminescent layer, a layer of radiation-unresponsive impedance elements over the photoconductive layer, a second electrode over the impedance layer, and a grid like third electrode extending between the luminescent layer and the impedance layer and contacting the photoconductive layer; means for maintaining a voltage difference V between the first and second electrodes, means for maintaining a voltage difference V between the first and third electrodes, V and V being different from zero and from each other, and means for varying the difference of V and V from each other.

2. Apparatus as set forth in claim 1 wherein V and V are direct-current voltages, and the varying means varies one of the magnitude and polarity of one of V and V 3. Apparatus as set forth in claim 2 wherein V and V have opposite polarities.

4. Apparatus as set forth in claim 3 wherein V has a'value atwhich, in the non-irradiated condition of the photoconductive layer, the luminescent layer luminesces due to V alone, and V has a value at which, in the irradiated condition of the photoconductive layer, the luminescent layer luminesces due to V alone.

5. Apparatus as set forth in claim 1 wherein V and V are alternating-current voltages and the varying means varies one of the amplitude and phase of one of V and V 6. Apparatus as set forth in claim wherein V and V have a phase difference of more than 90.

7. Apparatus as set forth in claim 6 wherein V has a value at which, in the non-irradiated condition of the photoconductive layer, the luminescent layer luminesces due to V alone, and V, has a value at which, in the irradiated condition of the photoconductive layer, the luminescent layer luminesces due to V alone.

8. Apparatus comprising a solid-state image intensifier; said intensifier including a first electrode, an electricfield-responsive luminescent layer over the first electrode, a radiation-responsive photoconductive layer over the luminescent layer, a layer of radiation-unresponsive impedance elements over the photo-conductive layer, a second electrode over the impedance layer, and a gridlike third electrode extending between the luminescent layer and the impedance layer and contacting the photoconductive layer; means for maintaining a voltage difference V between the first and second electrodes, means for maintaining a voltage difference V between the first and third electrodes, V and V being different from zero and from each other, and means for varying the difference of V and V from each other; said maintaining and varying means including a potential source connected to the second and third electrodes, and a variable impedance coupled between the third electrode and the first electrode.

9. Apparatus comprising a solid-state image intensifier; said intensifier including a first electrode, and electric-field-responsive luminescent layer over the first electrode, a radiation-responsive photoconductive layer over the luminescent layer, a layer of radiation-unresponsive impedance elements over the photoconductive layer, a second electrode over the impedance layer, and a gridlike third electrode extending between the luminescent layer and the impedance layer and contacting the photoconductive layer; means for maintaining a voltage difference V between the first and second electrodes, means for maintaining a voltage difference V between the first and third electrodes, V and V being different from zero and from each other, and means for varying the difference of V and V from each other; said maintaining and varying means including a source of alternating-current voltage, a first amplifier coupled between said source and the first and second electrodes, a second amplifier connected between said source and the first and third electrodes, and an adjustable phase-shifting device connected to at least one of said amplifiers.

10. Apparatus as set forth in claim 9 including means for adjusting the amplitude of the voltage in the circuit of the phase-shifting device.

11. Apparatus as set forth in claim 9 wherein a reversing switch is provided for reversing the voltage applied to at least two of the electrodes.

References Cited by the Examiner UNITED STATES PATENTS 2,916,630 12/59 Rosenberg 250213 2,975,294 3/61 Kazan et al. 250-213 3,070,702 12/62 Marko 250213 RALPH G. NILSON, Primary Examiner.

WALTER STOLWEIN, Examiner. 

1. APPARATUS COMPRISING A SOLID-STATE IMAGE INTENSIFIER; SAID INTENSIFIER INCLUDING A FIRST ELECTRODE, AN ELECTRIC-FIELD-RESPONSIVE LUMINESCENT LAYER OVER THE FIRST ELECTRODE, A RADIATION-RESPONSIVE PHOTOCONDUCTIVE LAYER OVER THE LUMINESCENT LAYER, A LAYER OF RADIATION-UNRESPONSIVE IMPEDANCE ELEMENTS OVER THE PHOTOCONDUCTIVE LAYER, A SECOND ELECTRODE OVER THE IMPEDANCE LAYER, AND A GRIDLIKE THIRD ELECTRODE EXTENDING BETWEEN THE LUMINESCENT LAYER AND THE IMPEDANCE LAYER AND CONTACTING THE PHOTOCONDUCTIVE LAYER; MEANS FOR MAINTAINING A VOLTAGE DIFFERENCE V2 BETWEEN THE FIRST AND SECOND ELECTRODES, MEANS FOR MAINTAINING A VOLTAGE DIFFERENCE V1 BETWEEN THE FIRST AND THIRD ELECTRODES, V1 AND V2 BEING DIFFERENT FROM ZERO AND FROM EACH OTHER, AND MEANS FOR VARYING THE DIFFERENCE OF V1 AND V2 FROM EACH OTHER. 